LVM (Logical Volume Manager) provides an abstract layer for disk management. Instead of using partitions, LVM uses Logical Volumes (LV).
The big advantages of using LVM are:
Have you ever had problem of free space on one partition and a lot of unused space on an other or on an other disk?
LVM can dynamically resize your LV.
Have you ever destroyed the wrong partition because you typed may be /dev/sda5 instead of /dev/sdb5?
LVM provides user like names for your LV.
Have you ever desired to use two or more HD on parallel for enhancing the performance without RAID?
LVM provides stripped LV, so that it writes/reads from/to more than one HD at the same time.